Krotoszyn city flag

Here is the flag of Krotoszyn city, in Krotoszyn county, Wielkopolskie
vojvodship, as presented at the city's
website, adopted ?
Flagdescription: brightblue, in top hoist the city arms.
Arms: azure bordered argent two keys in saltire between two 6-rayed
mullets or; in chief a 5-rayed mullet or charged with a flower argent.
Origin/meaning: The two crossed keys are the symbol of St. Peter, the
patron saint of the town. The roses are derived from the arms of the former
Lords of Krotoszyn, from the Rozdrazewskis family.
Source: Ralf Hartemink.
Jarig Bakker, 3 Mar 2008

What's the name of this particular kind of shield? A similar shape is
favoured by the President of Liberia and, not
unrelated, it is popular in the US, notable as the distintive graphic enclosure
for "U.S. Route"
highway number signs.
António Martíns-Tuválkin, 21 Mar 2008